The quench andtemper process induces enormous stresses, which can lead to part cracking during the process if good part design guidelines and proper heat treating practices are not followed. Baseline comparison showed that the austempered steel with a lower bainite microstructure exhibited higher hardness. In other words, the crack existed prior to austenitizing. Pdf effect of quenching and tempering treatments on impact. A common misconception is that quench cracks can occur only while the piece is being quenched. The martensitic transformation starts at the outermost surfaces of the part being quenched. With 4340 youd have a quenched part with a surface hardness around the lower mid 60s, but because the material is thru hardening, the remainder is going to be in the rc 5657 range most times, and at least rc55. For materials such as 4340, tempering must take place within 15 minutes of removal from the quench to avoid quench cracking. The quench cracking that occurs in steels with carbon contents greater than about 0. Inadequate material data can also result in conditions that may contribute to failure. Material and process selection can contribute to cracking as well. The graph bars on the material properties cards below compare quenched and tempered saeaisi 4340 to. Aisi 4340 steel is a medium carbon, low alloy steel known for its toughness and strength in relatively large sections. Quenched and tempered 4340 nicrmo steel quenched and tempered saeaisi 4340 is saeaisi 4340 steel in the quenched and tempered condition.
Mechanisms of fatigue crack initiation in annealed, quenched and. Tool designers must also be aware of the problems and difficulties in manufacture, heat treat ment, and use. Throughhardening low alloy steel bar 4340 atlas steels. Austenitize 1600 1650f 871 899c, liquid quench, temper. We will not be discussing the metallurgical properties of 4140 or trying to explain what happens to its microstructure when it cools too rapidly, just remember that the key is to control our cooling rate. If these stresses are acting in the same direction as the load applied in service, an. Avoid over heating and overly long dwell times while austenitizing. Otai special steel have more 16 years experience in 4340 steel plate, round bar, flat bar, square bar, hexagonal bar, sheet, pipe and worm gear supply. Inservice d2 toolsteel component failure due to quench cracking. Jasper5attributessuchcracks tothethermalgradientswhichexistduringquenching,but,as honda6. Finally, materials that are heat treated to high strength levels, even though they did not quench crack, may contain localized concentrations of high residual stresses. Using water as a quench media, for instance, can cause the material to warp as it cools. Risk of damage form the hardening quench cracks depth of hardening.
If there is decarb associated with a crack, that shows that the crack existed at the time the material was at temperatures hot enough to decarburize. Mar 28, 2012 certain highhardenability materials, such as 4340, are particularly prone to quench cracking and must be tempered immediately usually within 15 minutes of quenching to avoid problems. Aisisae 4340 alloy steel 4340 steel properties all metals. External corners need to at least be broken before heat treat, as they too are a stress concentration area. Because there are high capital expenditures involved with the installa. It is an alloy structural grade which used by the sae. They appear to bear no definite relation to any of the.
The soaking time in air furnaces should be 1,2 min for each mm of crosssection or 0,6 min in salt or lead baths. Welding is not recommended because of the danger of quench cracking. Any condition that concentrates the stresses encountered in quenching will promote the formation of quench cracks e. If i was faced with this situation and limited by existing air permits, i would instead try to locate a commercial heat treater with oil quenching capability. The crack is seen to travel along the prior austenite grain boundaries. This is to reduce likelihood of cracking during quench. In the quenching action, the steel is subject to nonuniform cooling, thermal deformation, and a phased grain transformation that can. For hammers, quench just as the color purple creeps up to the face. So, you now temper the part at say 300 to get your 62 case. If the use of water as quenching medium, 4140 steel cooling speed is faster at high temperature range, but the cooling speed is slow at low temperature range lower than the ms temperature.
This is due to the very high hardenability which causes a severe volume change gradient going from austenite to martensite through the thickness. Dec 15, 2009 the material must first be heated to the point where austenitization can occur, and then cooled rapidly enough to have the transformation into martensite take place, but avoid the possibility cracking. Cracked 4340 after quench metal and metallurgy engineering. Quenching can lead to warpingcracking and other issues with the material, even when it is done properly. It is crucial to control the environment in which the quenching is done to minimize the risk of damage to the material. Ive made hammers out of 4340 and tempered them by running the color and quenching in oil. Quench ing, therefore, is a very important process in the successful hardening of commercial heat treaters have not received any specific mandates from industry or government agencies to modernize their heat treating equip ment. C, followed by slow cooling no quench reducing the problem of distortion. Parts should be heated as quickly as possible to the austenitic temperature range 830 o c 860 o c and required case depth followed by an immediate oil or water quench, depending upon hardness required, workpiece sizeshape and quenching. Overheating during the austenitizing portion of the heat treatment cycle can coarsen normally fine grained steels. One cannot expect that nickel plating would be employed in the heat treatment of highstrength steels, since quench cracking is normally avoided by using oil as the quenching medium. Finally, materials that are heat treated to very high strength levels, even though they did not quench crack, may contain localized concentrations of high residual stresses. Good mechanical properties are required for aisi 4340 applications so heat.
If the use of water as quenching medium, 4140 steel cooling speed is faster at high temperature range, but the cooling speed is slow at low temperature range lower than the. Alloy steels are generally more adaptable to marquenching. Certain highhardenability materials, such as 4340, are particularly prone to quench cracking and must be tempered immediately usually within 15 minutes of quenching to avoid problems. Our largest furnace is capable of performing oil quench hardening with internal working dimensions of 36w x 72l x 42h. The temperatures are the same as those given for full annealing. From aisi 1045 to aisi 4340 the polymer quenching hardening heat treatment can be the solution for complex jobs. Quench cracks 3 ways to recognize quench cracks result from stresses produced during the transition from austenite to martensite, which involves an increase in volume. For chisels, take it to a straw to bronze color and quench.
See the chemical composition and physical properties of aisi 4340 quenched and tempered, find alternative materials, and connect with suppliers. I still think that after working with it and studying it for 42 years. For example, adequate fatigue data, elevatedtemperature tensile data, or creep or corrosion data. Material issues can usually be attributed to either selection of material or material imperfections rendering it unsuitable for service. Aisi 4340 steel is a medium carbon, low alloy steel. Commercial and military aircraft, automotive systems, forged hydraulic and other machine tool applications, forged steel crankshafts. Nitriding and carburizing are the two most common heat treatment practices for surface hardening functional components. So far this is about the only information i have gathered. In materials science, quenching is the rapid cooling of a workpiece in water, oil or air to obtain certain material properties. For highspeed steels, you want to cool to 120f to 150f 50c to 65c and then temperbut it is all too common to find loads sitting waiting for a temper furnace for up to a day. Atlas 4340 lowalloy steel bar complies with grade as1444, grade 4340 andor. If quench uniformity is required, such as in complying with the caterpillar 1e0106a or 1e0106b specification, polymer quenching is an excellent choice. Overview of the mechanisms of failure in heat treated steel. The main difference is that in nitriding, nitrogen atoms are made to diffuse into the surface of the parts being processed, whereas in carburizing, carbon is used.
This can leave remnants of seams or other surface imperfections which can act as a nucleation site for a quench crack. I should have used the oil quench tank to cool it off faster, but there was a reason i didnt. When i was in school, i learned that if a piece of steel is cooled too rapidly during the quench portion of a hardening heat treatment, it might crack. Since marquenching lowers the residual thermal stress, it is used for parts with complex geometries, diverse weights, and section changes. Marquenching is used primarily to minimise distortion and eliminate cracking. It was established that intergranular cracking observed in this alloy was caused during heat treating as the thread root served as an effective stress concentration and induced quench cracking. External corners need to at least be broken before heat treat, as they too are a. The following information gives an overview of 4340 steel properties. Aisi 4340 is also one kind of nickel chromium molybdenum steels. In this work quenching parameters in the aisi 4340 steel. The steel is then quenched at varying speeds to create the desired grain structure. However, as in motor shaft applications, under quenching and tempering conditions, 4340 steel typically use high preheating in low hydrogen processes.
In addition, a good correlation between the simulated and experimental results for quench distortions depends critically on the knowledge of. This material at my shop is quenched in 250f agitated oil without any issues. Distortion sensitive or crack prone if your parts are especially distortionsensitive or crack prone, thermtech will customtailor an oil quench process to minimize or eliminate these problems completely while still achieving the required material properties. Honda6andothershavefound,cracksdonotusuallyoccuruntil the steel hasreached ordinarytemperatures. Although hard, the material is extremely brittle and subject to cracking. Seams will contain crud and folds will have a decarb layer. Throughhardening low alloy steel bar 4340 colour code. I even made a larger hand hammer out of 4140 since this has happened and did a full quench on it and it didnt crack. Aisisae 4340 alloy steel, 4340, is a nickelchromiummolybdenum alloy steel known for its toughness and its ability to attain high strengths in the heattreated condition.
Parts can therefore be machined to near final size, leaving a grinding allowance only. Cracking during heat treat can be caused by several factors. Too much time between the quenching and the tempering of the heattreated parts. Quench cracks have an obvious high temp iron oxide in the crack. Jade band marigold introduction atlas 4340 is a nominally 1. Overload failure of a quenchcracked aisi 4340 steel. Aisisae 4340 alloy steel 4340 steel properties all. Aisi 4340 has a favorable response to heat treatment usually oil quenching followed by tempering and exhibits a good combination of ductility and strength when treated thusly. Nickel content provides a good combination of hardness and toughness.
After quenching, aluminum alloys are aged, and during. More difficult to heat treat than 1045 or4140 since it is prone to quench cracking. Mechanisms of fatigue crack initiation in annealed, quenched and tempered 4340 steel. The chemical composition of aisi 4340 is show in table 1. Quench cracking in steel as a case of hydrogen embrittlement.
Quench cracks 3 ways to recognize speaking of precision blog. It does this by reducing the window of time during which these undesired reactions are both thermodynamically favorable, and kinetically. Thisobservation eliminates purelythermal stresses, which disappear when the steel. Marquench hardening available in salttosalt or furnacetosalt.
Quench cracks 3 ways to recognize speaking of precision. I quenched and tempered the big 4340 beast, then had to wait a long time for it to cool down so i could use our portable brinell tester. And it has good toughness, fatigue resistance, impact toughness and etc. Saeaisi wrought steels top, all iron alloys middle, and the entire database bottom. Evaluation of toughness in aisi 4340 alloy steel austenitized at low and high temperatures robert o. Jan 04, 2009 so what material is best for a bolt on snout it seems in this industry everyone has their own opinion about materials. Polymer quenching is useful for a wide range of steels. Here are 7 ways that steel can fail as a result of quench cracking from heat treatment. Distortion and crack prediction and experiments in quenching.
As mentioned above, prehardened and tempered 4340 steel bars or plates can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness in excess of rc 50. The material must first be heated to the point where austenitization can occur, and then cooled rapidly enough to have the transformation into martensite take place, but avoid the possibility cracking. Yes, even in these days of nanomiracles, steel is still useful and interesting. This grade is not considered weldable by standard methods but it can be welded by more sophisticated methods such as ebw. Analysis of quenching parameters in aisi 4340 steel by.
After quenching in water, the material is the hardest it can get given the chemistry. Fine secondary cracks aligned transverse to the growth direction was revealed by scanning electron microscopy. If the steel is an oilhardening steel, the use of these overly aggressive quenchants will lead to cracking. Aisi 4340 steel, oil quenched 855c 1570f, 230c 450f. According to the actual production situation, we believe that the main reason of quenching crack of 4140 steel plate is. The high hardness of 4340 alloy steel requires that the material be welded in the annealed or tempered state and then heat treated to resist martensite formation and cold cracking. Quench cracking of steel cracking resulting from stresses produced during the austenite to martensite transformation during heat treating quenching and tempering. Uneven heating, overheating and excessive scaling should be avoided. Its like steaming green beans, then sticking them in cold water to stop them from cooking further. Making an improper selection of steel for the process.
Aisi 4340 alloy steel is heat treated at 830c 1525f followed by quenching in oil. You will need to take a section through the indication mount it and take a look under an electron microscope. Linkun is one of the leading china special steel manufacturers and suppliers, if you want to buy or import best highquality aisi 4340, 36crnimo4, 1. A comparison of fatigue properties of austempered versus. Pdf analysis of quenching parameters in aisi 4340 steel by.
Preheating and postweld heat treatment is desirable to prevent cracking and compromised mechanical properties. Nitriding is carried out at 490 o c 530 o c, followed by slow cooling no quench reducing the problem of distortion. Quenching can lead to warping cracking and other issues with the material, even when it is done properly. Oct 21, 2011 the 4140 bars came out fine, didnt need to retemper them. Hardening of steel is obtained by a suitable quench from within or above the critical range. Server it has been reported for asquenched aisi 4340 steel that high temperature austenitizing. While large 4140 rounds can be waterquenched, squares are a different story. Here are seven ways that steel can fail as a result of quench cracking from heat treatment. Overviewofthemechanismsoffailure in heat treated steel components. Sae aisi 4340 steel properties, heat treatment, equivalent. Usually, this is a sufficiently rapid quench to avoid formation of the soft ferrite phase during cooling.
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