Search results
Results from the WOW.Com Content Network
This produces steel that is much stronger than full-annealed steel, and much tougher than tempered quenched steel. However, added toughness is sometimes needed at a reduction in strength. Tempering provides a way to carefully decrease the hardness of the steel, thereby increasing the toughness to a more desirable point.
The quenching results in the formation of metastable martensite, the fraction of which is reduced to the desired amount during tempering. This is the most common state for finished articles such as tools and machine parts. In contrast, the same steel composition in annealed state is softer, as required for forming and machining.
Once removed from the oven, the workpieces are often quickly cooled off in a process known as quench hardening. Typical methods of quench hardening materials involve media such as air, water, oil, or salt. Salt is used as a medium for quenching usually in the form of brine (salt water). Brine provides faster cooling rates than water.
However, quenching certain steel too fast can result in cracking, which is why high-tensile steels such as AISI 4140 should be quenched in oil, tool steels such as ISO 1.2767 or H13 hot work tool steel should be quenched in forced air, and low alloy or medium-tensile steels such as XK1320 or AISI 1040 should be quenched in brine.
The most notable difference between austempering and conventional quench and tempering is that it involves holding the workpiece at the quenching temperature for an extended period of time. The basic steps are the same whether applied to cast iron or steel and are as follows:
non-alloy semi-finished (not finally annealed) E " alloy semi-finished (not finally annealed) K (=D+E) " non-alloy and alloy electrical steel sheet/strip in the semi-processed state N " for normal grain oriented products P: 1.7 T @50 Hz high permeability grain oriented S" conventional grain oriented
18–8 (304) stainless steel annealed: 200 HB [3] Quenched and tempered steel wear plate: 400-700 HB Hardened tool steel: 600–900 HB (HBW 10/3000) Glass: 1550 HB
This process is often used for knife making, by heating only the edge of a previously quenched and tempered blade. When edge turns the proper color temperature, it is quenched, hardening only the edge, but leaving most of the rest of the blade at the lower hardness. The knife is then tempered again to produce the final differential hardness. [16]