CWB level 3 Module 21 practice questions and answers graded A+ 2023/2024

CWB level 3 Module 21 practice questions The maximum solubility of carbon in a iron is: (a) 2%. (b) 0.002%. (c) 0.02%. (d) There is no solubility. - correct answer (c) 0.02%. True or false? When a steel is heated into the austenite region, all carbon and most other compounds dissolve to form a single phase. - correct answer True True or false? Pearlite is a single phase. - correct answer False What is the resulting structure of a 0.6% carbon steel slowly cooled from 900°C to room temperature? - correct answer About 25% proeutectoid ferrite and 75% pearlite Most fine grain steels retain their fine grains: ( (a) up to the melting temperature. (b) up to the grain coarsening temperature, but above that behave as coarse grain steel. C (c) only up to the transformation temperature. - correct answer (b) Why is martensite produced rather than pearlite when a steel is rapidly quenched from, 900°C? - correct answer Insufficient time for carbon to diffuse to form carbides The hardness of martensite depends mainly on the: (a) alloy content. (b) rate of cooling. (c) carbon content. (d) size of the part. - correct answer (c) Can bainite normally be produced in continuous cooling of a plain carbon steel? - correct answer No Increasing the carbon content: (a) lowers the martensite start temperature M. (b) raises the M. (c) has no effect on M. - correct answer (a) lowers the martensite start temperature M. Calculate the ideal critical diameter (hardenability) for a steel with 0.2%C, 0.25%Si, 1 .0%Mn, 0.5%Cr, 0.5%Mo, 1.0%Ni (assume an initial grain size of ASTM 8). Use section 2.5.3 and 2.5.4 as a reference. - correct answer 5.0 Using Figure 2.34, estimate the fastest rate a weld could cool without the HAZ becoming harder than 350 HV for a steel of 0.2%C, 0.18%Si, t2%Mn, 0.35%Cr. - correct answer 30C/s at 540 C What happens to the carbon trapped in the tetragonal structure when martensite is tempered? - correct answer The carbon is released Secondary hardening during tempering results from: (a) retained austenite. (b) a slow heating rate. (c) the presence of strong carbide formers. - correct answer (c) the presence of strong carbide formers. 4. If a thermal stress relief is applied to a welded quenched and tempered steel, the temperature should not exceed the: (a) transformation temperature. (b) original tempering temperature. (c) grain coarsening temperature. - correct answer (b) original tempering temperature. The effect of increasing the carbon content of a steel on the Charpy transition curve is to: (a) lower the transition temperature. (b) raise the upper shelf. (c) raise the transition temperature and lower the upper shelf. - correct answer (c) raise the transition temperature and lower the upper shelf. What simple heat treatment is widely used to improve the toughness of structural steels? - correct answer Normalizing If plates are deformed more than 5% during fabrication, the simple heat treatment often specified to restore ductility is: (a) a full furnace anneal at 900°C. (b) normalization. (c) stress relief, typically at 635°C. - correct answer (c) stress relief, typically at 635°C. The main purpose of using a lower finishing temperature during controlled rolling of steel is to: (a) limit re-growth of austenite grains. (b) allow time for precipitates to dissolve. (c) reduce the force necessary for rolling. - correct answer (a) limit re-growth of austenite grains. The austenite grain size close to the weld interface (fusion boundary) is determined mainly by the: C