Tempering, Mechanical Engineering

TEMPERING:

The hardening treatment specified to steel raises the hardness but initiates internal stresses due to different cooling rates. The internal stresses are created also due to transformation from austenite to martensite. Tempering treatment intends at decrease these stresses. The treatment comprises in heating the hardened component to in between 200oC and 600oC and holding this at such temperature for a predetermined period of time and after that cooling gradually to room temperature. Because martensite itself is meta-stable phase, structural changes induced via tempering proceed fairly quickly. Each structures resulting from tempering are termed martensite. Modifies occurring during several temperature ranges are explained below as:

100o - 220oC

Extremely little change happens in the micro-structure.  Though, this heating assists remove considerable internal amount of stresses. The stress relieving treatment is known while maximum hardness is needed and brittleness is not a problem. The strain is relieved due to removal of carbon atoms from their trapped locations.

240o - 400oC

During this range martensite decomposes fast into emulsified form of pearlite termed as secondary troostite. This material is extremely fine in nature and thus offers good shock resistance. The suitable edge tools are tempered in such range but more exactly inside 270oC-300oC.

400o - 550oC

The precipitate troostite initiates for coalesce forming a coarser from of globular pearlite termed as sorbite. This may be recalled both sorbite and troostite are here preferably called tempered martensite. This treatment is required in such components as springs, axles and beams.

600o - 700oC

Heating hardened steel during such range causes spheroidisation, the structure being termed as spheroidite. Such structure is formed caused by further coalescence of the carbide inside the alloy. Spheroidised steels represent fairly good machine-ability as the hard carbide particles are embedded within the soft ferrite matrix and thus do not have to be cut with the cutting tool. If the spheroidised steel is heated to immediately above its lower critical temperature the pearlite here will alter to austenite and cooling to room temperature will yield a lamellar pearlite structure plus pro- eutectoid ferrite or cementite depending on carbon content.

Moderating the temperature of tempering via colour appearance is a tradition that is supportive on shop floors. Though, for accuracy the precise temperature measurement are to be preferred. Table explains the colour appearance and temperature in link along with various tools.

Table: Tempering Temperature and Colours of Tools

Tool

Temperature oC

Colour

Planning tools

230

Paste straw

Milling currents

240

Dark straw

Taps and dies

250

Brown

Punches, drill bits

260

Purplish-brown

Press tools

270

Purple

Cold chisels

280

Dark Purple

Wood saws, springs

300

Blue

Posted Date: 2/26/2013 6:00:10 AM | Location : United States







Related Discussions:- Tempering, Assignment Help, Ask Question on Tempering, Get Answer, Expert's Help, Tempering Discussions

Write discussion on Tempering
Your posts are moderated
Related Questions
what are the tests to carried out after mockup preparation

Computers control system in flexible manufacturing system

advanced cam profile synthesis

A steel rod of 20 mm diameter passes centrally through a copper tube of 50 mm external diameter and 40 mm internal diameter. The tube is closed at each end by rigid plates of negli

The following guidelines are intended to assist the HVAC lead, designer or auditor in preparing an assessment of the quality of the HVAC engineering work for a specific project. T

which aero-gas turbine engine is used in T5 aircraft

Tropical geometric information of solids A face is surrounded by a set of vertices. Using the right-handed rule, the ordering of these vertices for describing a particular face

if motion of the belt is reversed, how the law of the belting shall be violated??

A copper bar 80 mm by 60 mm in cross-section (k = 370 W/m ºC) is lying in a insulated trough so that the heat transfer from one face both the edges is negligible. It is seen that w

Calculate the vertical deflection: Calculate the vertical deflection at the tip of the cantilever shown in Figure Figure Solution Measuring the distance x f