A heat treatment that reheats quenched steel to a temperature below the A1 temperature (727 °C). It restores toughness and reduces internal stresses at the cost of some hardness.
Japanese name: 焼戻し
Tempering appears in 4 practice questions across 4 topics, including Heat treatment and metallic materials, Metals and alloys, Surface treatment and tribology.
When as-quenched martensite is heated, it changes in stages depending on temperature. As a rough guide, at about 100–250 °C supersaturated carbon precipitates as fine carbides such as ε-carbide and the tetragonal distortion of the lattice decreases. At about 200–300 °C retained austenite decomposes, and above about 250 °C cementite forms and the matrix approaches ferrite. In steels containing Mo, V, W or Cr, fine alloy carbides precipitate above 500 °C, causing secondary hardening, a temporary rise in hardness.
The higher the tempering temperature and the longer the time, the lower the hardness and the higher the toughness. Parts that need hardness and wear resistance, such as cutting tools, bearings and carburized parts, keep a high hardness with low-temperature tempering at about 150–200 °C. Machine parts such as shafts and gears that need both strength and toughness receive high-temperature tempering at about 550–650 °C; combined with the preceding quench, this is called quenching and tempering. The effects of temperature and time can be treated together with a tempering parameter of the form T(C + log t) (C is about 20 for steels).
Depending on the tempering temperature, toughness can actually drop. Tempering at about 250–400 °C causes tempered martensite embrittlement, in which carbides precipitate as films at martensite lath boundaries and impact energy falls, so tempering in this range is usually avoided. Also, when Ni–Cr steels and others are cooled slowly through or held in the range of about 375–575 °C, temper embrittlement occurs as impurities such as P, Sb and Sn segregate to prior-austenite grain boundaries. It is prevented by rapid cooling after tempering, reducing impurities, adding Mo and similar measures.
As-quenched steel has large internal stresses and can crack some time after quenching if left standing (delayed cracking), so it is tempered as soon as possible after quenching. Steels with much retained austenite, such as high-speed tool steels, are tempered two or three times at around 550 °C, converting the retained austenite to martensite and then tempering that martensite. For precision parts such as gauges and bearings, where dimensional stability matters, a subzero treatment cooling below 0 °C may be added after quenching before tempering.
Answer: C. To restore toughness and reduce internal stresses at the cost of some hardness
As-quenched martensite is hard but very brittle and carries large internal stresses. In tempering, the steel is reheated to a temperature below the A1 temperature (727 °C); the supersaturated carbon precipitates as fine carbides and internal stresses relax, so hardness falls but toughness recovers substantially. The higher the tempering temperature, the softer and tougher the structure; low-temperature tempering is used for tools and high-temperature tempering for machine parts (the combination with the preceding quench is called quenching and tempering). An increase in hardness on tempering is limited to secondary hardening in certain alloy steels and is not the general purpose. Tempering tends to decompose retained austenite; increasing it is not the aim.
Tempering reheats quenched steel to a temperature below the A1 point to restore toughness. Annealing usually heats steel above the A1 or A3 point and cools it slowly to soften it or refine its structure, and it does not presuppose quenching.
It is a treatment in which quenching is followed by tempering at a high temperature of about 550–650 °C to balance strength and toughness. It gives a tempered martensite structure and is widely applied to shafts and gears of machine structural steels such as S45C and SCM435.
Yes. In tool steels containing Mo, V, W and similar elements, fine alloy carbides precipitate around 500–600 °C, causing secondary hardening. Hardness can also rise when retained austenite transforms to martensite on cooling.
In tempering, the steel is reheated to a temperature below the A1 temperature (727 °C); the supersaturated carbon precipitates as fine carbides and internal stresses relax, so hardness falls but toughness recovers substantially.
What is the main purpose of tempering a quenched steel?Its strength can be adjusted by quenching and tempering, and it is widely used for shafts and gears.
What does the JIS steel designation “S45C” stand for?HSS gets its hardness from quenching and tempering, so heating above the tempering temperature softens it, and requenching also raises problems of dimensional change.
Cutting tools are coated with hard films such as TiN. Which…However, when it breaks, the strain energy stored inside shatters the whole sheet into small granules, and it cannot be cut after tempering.
Which correctly describes how sheet glass is strengthened b…Martensite Tempered glass Hall–Petch relationship Hardenability Precipitation hardening